This invention relates to a system for producing ultrapure water and to the ultrapure water product so-produced. More particularly, this invention relates a water purification system capable of removing organic and ionics species from water to produce ultrapure water.
At the present time, analytical instruments, including high performance liquid chromatography (HPLC) ion chromatography (IC) and inductively coupled plasma mass spectroscopy (ICP MS) detect the type and the concentration of anions and cations in liquid samples. A convenient method for measuring the concentration of various specific ions is to compare the unknown sample which has been subjected to analysis to a blank standard liquid and standards of known ion concentration. The unknown sample contains various specific ions of unknown concentrations. The blank standard is known to have a very low ion concentration. The ion standards are the same blank standard with known concentrations of specific ions added. The comparison of the unknown sample, blank standard and ion standards can be used, for example in a chromatographic separation process to determine ion concentrations in the unknown sample.
A limitation in this comparison procedure is imposed by the ion concentration in the blank standard. The blank standard also must be free of gas bubbles to prevent interference with ion concentration measurement. The lower limit of ion concentration which can be measured in the sample is limited by the ion concentration in the blank standard. Thus, the user of the chromatographic process cannot determine the concentration of ions in the sample which is lower than the concentration of ions in the blank standard. At the present time, the pure water utilized as a blank standard contains about fifty parts per trillion (ppt) of total anions and cations. In addition to the purity of the water being limited to about 50 ppt, the storage of water in a container either before use or within the system provides a site for bacteria growth which contaminates the water.
At the present time, a method for producing ultrapure water for use as a blank standard comprises passing a source of deionized water through a series of beds, usually between four and six beds, containing a mixture of cation exchange resin beads and anion exchange resins beads which, optionally, can include particulate activated carbon. The purified water obtained from the series of deionizing beds is then directed to a water storage step such as a 20-50 liter Nalgene (high density polyethylene) bottle which introduces only a very low level of contaminating ions into the water. In a preferred procedure, the atmosphere in the storage bottle comprises an inert gas such as helium. After the desired amount of water has been introduced into this purification system, the system is closed to additional deionized water feed. The water within the system then is recirculated from the storage area through the series of beds and back to the storage area, usually for about 6 to 24 hours. In this manner, ions are continuously removed from the water to produce ultrapure water having an ion concentration as low as about 50 parts per trillion. This ultrapure water then can be used as a source of blank standards in chromatography systems.
Accordingly, it would be desirable to provide a system for producing ultrapure water having an ion concentration less than about 50 ppt and preferably less than 10 ppt. Furthermore, it would be desirable to provide such a system which eliminates the need for storing of purified water thereby eliminating a potential source of bacteria growth. Furthermore, it would desirable to provide such a system which eliminates gas bubbles in the water that may interfere with instrument measurement of ion concentration.